Callen and Sam are trapped in an armed submarine that terrorists are using to try and blow up an aircraft carrier. The situation turned worse as they lost contact with their team and now are running out of time as their team tries to locate them to foil the terror attack.

The premiere episode of CBS's police procedural drama will be a continuation of the season five cliffhanger finale, as Callen and Sam will realise that in order to avert the fatal event they have to die, showrunner Shane Brennan teased.

"We jump right in," Brennan told TV Line. "We left Sam and Callen stuck in a drug cartel sub that was [filled to the gills with ammonium nitrate] and we come back right on top of it. It's just continuous action. It's a very, very intense opening episode, and at one point both Callen and Sam realise that in order to stop what they've discovered is a terrorist attack, they will have to, in fact, die. So it's pretty full on."

The official synopsis of episode one Deep Trouble Part II via Zap2it reads:

"Callen and Sam are trapped in an armed submarine that terrorists have aimed to hit an aircraft carrier in San Diego. Meanwhile, Hetty defies orders and forgoes her trip to Washington, as the team tries to locate and save Callen and Sam and prevent the terrorist attack."

The premiere episode will also focus on Hetty's struggle as she heads to Washington to be questioned by the Senate society for her failed Afghanistan mission.

Hallels speculates that director Vance will be sceptic towards Hetty as he suspects she leaked the classified information about the secret operation.

Expect high voltage drama from the season six premiere on CBS on Monday night.

In case you missed the episode during its airing time, click here to watch the episode online the very next day on CBS' official website.